An image sensor is a device that can convert an optical image into an electronic signal. Image sensors are commonly used in still cameras, video cameras, video systems, and other imaging devices. Cameras and other imaging devices generally employ either a charge-coupled device (CCD) image sensor or a complementary metal-oxide-semiconductor (CMOS) image sensor.
CMOS image sensors include an array of light-sensitive pixel cells each of which is typically configured to output an analog voltage that is indicative of light incident on the light-sensitive pixel cell. A CMOS image sensor can further include additional circuitry to convert the analog voltage to digital data, such as analog-to-digital converters (ADCs). Thus, a CMOS image sensor can be an integrated circuit that comprises various analog, digital, mixed-signal, etc. components associated with capturing light and processing imaging related information. Accordingly, a CMOS image sensor can be a system on chip (SoC). For example, components integrated into the CMOS image sensor oftentimes include a processor module (e.g., microprocessor, microcontroller, or digital signal processor (DSP) core), memory, analog interfaces (e.g., analog to digital converters, digital to analog converters), and so forth that may be implemented in a same integrated circuit package. A CMOS image sensor can include multiple supporting blocks that can provide timing control, clock drivers, reference voltages, analog to digital conversion, digital to analog conversion, key signal processing elements, and the like.
Imaging systems implemented using CMOS image sensors can reduce costs, power consumption, and noise while improving resolution as compared to other types of image sensors. High-performance video cameras can thereby be assembled using a single CMOS integrated circuit supported by few components including a lens and a battery, for instance. Accordingly, by leveraging CMOS image sensors, camera size can be decreased and battery life can be increased. Also, dual-use cameras have emerged that can employ CMOS image sensors to alternately produce high-resolution still images or high definition (HD) video.
Recent trends in imaging are evolving toward capture of still images and video at high-frame rates (e.g., 120 frames per second or greater), in ultra-high-resolution (e.g., 3840 by 2160 pixels or greater), and/or with a per-pixel high dynamic range. To meet these demands, conventional CMOS image sensors have generally incorporated a greater number of ADCs and/or higher frequency ADCs to meet faster data rates needed to increase frame rate or resolution, or higher-resolution ADCs to increase the per-pixel dynamic range. Generally, however, increasing the number, frequency, or sampling resolution of ADCs in a CMOS image sensor increases the power required to operate the CMOS image sensor. In some applications, such as handheld still-image or video cameras, the increased power draw reduces battery life. In other applications, such as space-based, airborne, or automotive platforms, increased power requirements of a CMOS image sensor may be prohibitive if a power source used to operate the CMOS image sensor cannot deliver the required power.